A vinyl acetate-ethylene copolymer emulsion stabilized with polyvinyl alcohol has been used by the carpet industry as an adhesive for tufted carpet manufacture since about 1970. Such copolymer had a Tg in the range of -15.degree. to -18.degree. C. and contained 5% polyvinyl alcohol based on vinyl acetate. The polyvinyl alcohol stabilizer system comprised a mixture of low viscosity partially hydrolyzed polyvinyl alcohol and medium viscosity partially hydrolyzed polyvinyl alcohol. The emulsion was about 52% solids and had a Brookfield viscosity of 500 cps. The emulsion demonstrated adequate performance in the carpet backing application although the water resistance was less than desired.
With the advent of newer, modern methods of carpet backing manufacture, including higher calcium carbonate loadings and frothing the adhesive compound, the vinyl acetate-ethylene copolymer emulsion was becoming an obsolete product. The emulsion could not be compounded to the higher calcium carbonate loadings and was not compatible with all grades of calcium carbonate nor with styrene-butadiene emulsions.
U.S. Pat. No. 4,239,563 discloses such vinyl acetate-ethylene copolymer emulsions having a Tg between about -35.degree. C. and about -10.degree. C. as laminating adhesives for rugs and carpets. The amount of vinyl acetate in the copolymer of the emulsion is between about 20 and 70 parts by weight and the corresponding amount of ethylene in the copolymer is between 30 and about 80 parts by weight. The copolymer emulsions can be prepared with or without surfactants. When polyvinyl alcohol is used as a protective colloid during the polymerization, it is not necessary to add a surfactant. If such a protective colloid is not employed, a surfactant such as a nonionic or anionic surfactant can be employed.
Prior art regarding vinyl acetate-ethylene copolymer emulsions prepared in the presence of polyvinyl alcohol includes the following:
U.S. Pat. No. 3,661,696 discloses a process for the production of an aqueous emulsion of an ethylene-vinyl acetate copolymer wherein the polymerization is performed in the presence of a preformed seed emulsion and a minor amount, from 1.5 to 6 wt %, of a protective colloid comprising a mixture of fully and partially hydrolyzed polyvinyl acetate. The resulting emulsion can be used as an adhesive. In Example 9 several emulsion compositions were prepared using the polyvinyl alcohol mixture in combination with a nonionic surfactant. In U.S. Pat. Nos. 3,734,819 and 3,769,151 a similar process is disclosed in which the ethylene-vinyl acetate polymer is prepared in the presence also of a small amount of a vinyl sulfonic acid comonomer or an unsaturated C.sub.3 -C.sub.6 acid, respectively. Similarly, these patents show emulsion compositions prepared using a seed emulsion, the polyvinyl alcohol mixture and a nonionic surfactant.
U.S. Pat. No. 3,692,723 discloses aqueous dispersions and heat melting adhesives comprising same, which dispersions contain a copolymer of ethylene and vinyl acetate wherein the ethylene content is from 30 to 98 wt %, the copolymer having been prepared by a copolymerization process utilizing a particular combination of nonionic emulsifier, anionic emulsifier and protective colloid.
U.S. Pat. No. 3,816,362 discloses a process for preparing a stable aqueous ethylene-vinyl ester copolymer emulsion having an ethylene content of 4 to 20 wt %. Example 1 shows the use of a polyvinyl alcohol, a polyoxyethylene nonylphenyl ether (nonionic surfactant) and sodium dodecyl benzene sulfonate (anionic surfactant).
U.S. Pat. No. 3,827,996 discloses aqueous dispersions of vinyl ester polymers containing as a protective colloid partially hydrolyzed polyvinyl alcohol having an average vlnyl acetate content of 5 to 7 mole %. The polyvinyl alcohol may consist of a blend of two or more polyvinyl alcohols, each of which has an average vinyl acetate content different from the average of the blend. Several examples show the use of a partially hydrolyzed and a fully hydrolyzed polyvinyl alcohol in combination with a nonionic surfactant in the preparation of vinyl acetate-ethylene copolymer emulsions.
U.S. Pat. No. 4,043,961 discloses adhesive compositions consisting essentially of an aqueous emulsion of vinyl acetate-ethylene copolymer prepared in the presence of protective colloid comprising fully hydrolyzed vinyl alcohol copolymer containing methyl methacrylate. The examples show the use of such vinyl alcohol copolymer in combination with a medium and/or low viscosity partially hydrolyzed polyvinyl alcohol and a nonionic surfactant.
U.S. Pat. Nos. 4,267,090 and 4,287,329 disclose the preparation of vinyl acetate-ethylene copolymer emulsions in a reaction medium containing a protective colloid and a surface active agent.
U.S. Pat. No. 4,521,561 discloses the preparation of vinyl acetate-ethylene copolymer emulsions exhibiting both partially- and fully-hydrolyzed polyvinyl alcohol compatibility prepared in the presence of a polyvinyl alcohol stabilizing system having an 8 to 10 mole % residual vinyl acetate content.